Process for producing cast iron of any desired structure



Feb. 11, 1930. F GREINE 1,746,467

PROCESS FOR PRODUCING CAST IRON OF ANY DESIRED STRUCTURE h Filed Nov. 6, 1926 2 Sheets-Sheet 1 F. GREiNER Feb. 11, 1930.

PROCESS FOR PRODUCING CAST IRON OF ANY DESIRED STRUCTURE Filed Nov. 6, 1926 2 sheets-shee 2 Patented Feb. '11, 1930 UNITED STATES PATENT' OFFICE FRITZ GBEINER, OF GANNSTATT/STUTTGABT, GERMANY PROCES FOR PRODUCING CAST IRON OF ANY DESIRED STRUCTURE Application filed November 8, 1926, Serial No. 146,801, and in Germany November 6, 1925.

The known process for obtaining cast iron of apredetermined structure by selecting the proportions of carbon and silicon content in the same with the aid of a diagram that is based on. theoretical considerations (see Kruppsche Monatshefte 1924, page 115) has the disadvantage that it can be practically applied only for narrowly limited thicknesses of walls, because in this process no allowance is made for changes due to the varying speeds .at which walls of different thicknesses .cool off, and these changes have a considerable effect on the properties of the castings pro.- duced. .The other known process for producing more particularly cast iron of a perlite structure by preheatlng the molds to an extent that depends on the thickness of the walls of the casting (see German Patent 417,689) is costly and is coupled with considerable technical difiiculties, particularly when the castings are large. Neither of these processes constitutes a means for obtaining a uniform structure in castings having walls of very different thicknesses and the latter process only provides a method for obtaining a perlite 7 structure which is by no means in all cases the kind of structure that.has the most favorable properties obtainable in a casting, because for strength for example the basic structure is of less importance than the quantity and nature of the graphite secretion. And in many instances,

properties, the founder desires to produce not perlite but ferritic iron for example.

The process according to the present invention enables the practical founder to obtain any desired structure of iron by selecting a content of (3+ Si that depends on the thickness of walls of the casting to be made.

The invention is illustrated in the drawing in which Fig. 1 is a diagram in which the relation between thickness of walls, content of C+ Si and structure for standard sorts of ey cast Eon is given by fields, partitioned o by four nes.

Figs. 2 and 3 show a side view and a cross section respectively of a motor engine cylinder and as in the case of castings which must be easy to work or have magnetic I Fig. 4 is a section of a fragment ofFig. 3 v on an enlarged scale.

In Fig. 1 the wall thicknesses of the castings obtained are indicated by the abscissae and the ordinate is a measure of the contents of C+Si corres onding to the different wall thicknesses. T e four lines, of which, in the main, two are straight and two bent, demarcate five fields I, II", II, II", III which correspond to structures of difi'erent and intermediate kinds.

Field I represents white cast iron, field IItrcpresents mottled cast iron, field II represents perlitic cast iron,- field II represents an intermediate structure between perlitic and ferritic cast iron, and field III represents ferritic cast iron. If the thickness of the walls of the casting to be made is iven and the desired structure of the same 1s known, the limits between which the total content of C+Si must lie can be. immediately ascertained from the diagram Fig. 1. The diagram also shows whether it is at all possible to produce the structure in question at the given thickness of wall and by the ordinary method of cooling. It is thus seen that the novel process renders it possible to produce, within wide limits and without any preheating of the mold, any desired structure at a given thickness of wall, i. e. it'enables a perlite, ferritic, mottled, or white cast iron to be obtained according to requirement.

A further drawback of previously known processes is that in the case of complicated castings having walls of very different thicknesses the question as to what thickness of wall should serve as a criterion for the classification or predeterminationof the structure of the iron could not be satisfactorily answered at all. Thus in cylinders of motorcar engines-the thickness of the wall of the internal or piston cylinder is much greater than that of the water jacket casing which latter has only to resist the pressure of the water. In such a casting the differences in the thickness of the walls may be between 3 and 20. ms. As the strength of the part that has to resist the reatest stress is the criterion for the utility of the casting, it is of course necessary in this case to select the kind of structure required for the thickest wall, and then the question arises as to how the thinner walls are to be made or maintained capable of being tooled.

From the diagram, Fig. 1, it can be seen at a glancebetween what wall thicknesses a casting of uniform structure throughout can be obtained, or what composition must be selected to obtain, if necessary, the same structure, say perlite, in the thickest and thinnest walls. But in many cases it will be found that the thicknesses of the. walls differ too much to enable this result to be achieved; for the diagram shows that when the different thicknesses are 3 and 20 mms., for example, it is not possible by mere choice or predetermination of a desirable composition to cast a perlite structure in both walls at the same time. Even if the hi hest permissible contentof C+ Si were se ected, the iron in the thinner 3 millimeter wall would turn white when it solidified, so that it could not be worked. In such cases the thinner parts, by the aid of the diagram, Fig. 1, are made of such thickness at the points where they have to be machined, or where their structure has to be of a certain kind that on solidification the same structure is formed at these points as in the thicker walls of the casting. This novel process thus enables the designer to tell beforehand down to what thickness of wall he may go without impairing the desired physical properties of the casting, and at points where the walls could be made thinner as far as their strength is concerned but must be made thicker for other reasons he simply makes them thicker. If this is not permissible the wall is first cast thicker at the point in question and the superfluous thickness is subsequently cut down by tools.

As a specific example of an application of the process, the production of the cylinder of an internal combustion engine or motorcar engine in accordance with the invention will now be described.

'The thickness of the piston cylinder 0 is assumed to be 20 mms. and that of the mantel rib b 3 mms. Assuming that the upper limit of (1+ Si which can be used in this case, having regard to strength, is 4.8%, it will be seen that a perlitic structure which will be capable of being machined cannot be obtained in a wall as thin as 3 mms; the thickness must be not less than 10 mms. But as it is only necessary to tool the outer edge of the rib I), only this part of rib b is made thicker and its other parts can be left so thin that, without their utility being interfered with, theywill turn white and be inca able of being tooled when they have cooled own after casting. Hence the lower edge of the rib .b, Fig. 4, is cast thicker to bring it up to 10 mms. and the superfluous thickness 0 is subseqpently machined off. If a subsequent mac ining off is not possible the necessary thickening is effected at another contiguous point where it does not interfere in any Way and can therefore remain.

Since the structure formation as a function different wall thicknesses, to produce the same I microstructure in walls of different thickness, which comprises using for the casting mixtures having a content of (3+ Si regulated in accordance with a chart on which percent of C+Si is plotted against wall thickness, said chart being divided into fields corresponding to the different classes of microstructure and defined by curves converging substantially toward the point whose coordinates are 0 mm. wall thickness, 7.0% (1+ Si, from the various points along the line 4.0% 0+ Si representing the wall thicknesses 6.0 mm. 12.5 mm. 51.5 mm. and 63. 5 mm. the content of 0+ Si being selected so that the crossings of the line representing said content by the lines representing the two extremes of wall thickness in question both lie in a single field of said chart. 1 I

2. The method of making a casting having diflferent wall thicknesses, to produce the same microstructure in walls of difi'erent thickness, which comprises using for the casting mixtures having a content of 0+ Si re lated in accordance with a chart on whic percent of C+Si is plotted against wall thickness, said chart being divided into fields corresponding to the different classes of microstructure and defined by four curves, two of said curves runnin substantially straight from the points havmg the coordinates 4.0%

C+Si, 6.0 and 12.5 mm. wall thickness, respectively, to the point having the coordinates 7.0% (3+ Si, 0 mm. wall thickness, the other two curves runnin from the points havmg the coordinates 4.0% C+ Si, 51.5 and 63.5 mm. wall thickness, respectively, to the points having the coordinates 6.7% C-l-Si, 12.5- and 17.5 mm. wall thickness, and from said last-mentioned points substantially straight toward the point whose coordinates are 7.0% C Si, 0 mm. wall thickness, the content of C+Si being selected so that the crossings of the line representing said content by the lines representing the two extremes of wall thickness in question both lie in a single field of said chart.

3. Process of makin a casting in accordance with claim 1 in w ich any parts of the substantially straight 4 missable content of C Si, are cast with walls of G-i-Si is sufficiently thicker to fall within the proper field of the diagram.

4. The method of making a casting having different wall thicknesses, to produce the same microstructure in walls of difl erent thickness, which comprises using for the casting mixtures having a content of C+Si regulated in accordance with a chart on which percent plotted against wall thickness, said chart being divided into fields corresponding to the different classes of microstructure and defined by curves which rise and converge in approximately straight lines to ward the point whose coordinates are 7.0% C+Si, 0 mm; wall thickness, the content of C'+ Si being selected so that the crossings of the line representing said content by the lines representing the two extremes of wall thickness inquestion both lie in a single field of said chart.

In testimony whereof I have aflixed my 

